Until Chang'E 3, only one lander capable of taking an image has been on the lunar surface since Apollo 17... that was Lunokhod 2. I am not aware of any images by either Lunokhod that showed the Earth. So you are correct.

That's good news! So where to now? Last I heard they were interested in the pyramidal crock on the rim of crater to the west. This area should give good exposures of local bedrock.

Again last I hear, the rover covered 40 m since landing. They should be able to do at least that this time, perhaps more. Other than the crater rim what over targets are there available in the area? I can think of a GPR traverse across the wrinkle ridge and contrasting analyses between the low and high Ti-basalt flows.

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"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

I'm not sure I get how the data is presented in the 'cubical' spectrograph. AIUI, each heat map face corresponds to one of the two spectrometers (let's say the top face is the Visible, and the one on the right the NIR). The redness/blueness on the heat-map corresponds to the intensity in a particular frequency bin. A pixel on the heat-map face at a distance x from the common edge between that face, and the image face corresponds to an image pixel at the same distance x, from the same edge, on the image face. So, in order to get the full information collected by the instrument, we'd need a movie of the heat-map faces, where successive frames represent the intensities in neighbouring frequency bins.

Also, does anyone know why Yutu is carrying a GPM, and not a reflection seismometer? Couldn't the latter function in a dual purpose mode? In a nominal/low power mode of doing seismology; and in a high-power mode -- serving as a potential rover extricator -- through forced acoustic compaction of loose regolith that may trap the rover (a la Spirit)? Or even prophylactic compaction - sort of expanding the envelope of terrain that the rover can traverse.. (technically, changing the mechanical characteristics of the terrain through perturbation is bringing previously off-limits regions into the envelope of possible exploration sites, but then again - you're not changing the composition and mineralogy)

No, each face of the cube is an image of the surface in that wavelength. Follow one pixel all the way down the stack and you get a spectrum for that pixel.

As for the seismometer - what you describe sounds far too complex and energy-intensive for a small rover, possibly even potentially harmful to the rover, and I think the data would be far less able to resolve near-surface structures.

No, each face of the cube is an image of the surface in that wavelength. Follow one pixel all the way down the stack and you get a spectrum for that pixel.

The top right corner of the image kind of nudges you toward that interpretation doesn't it? The columns of cool colours, despite the common edges having both bright and dark parts... I thought that, but then the complexity of colour perception, and the narrow spectral band that we perceive as visible played on my mind, and I thought something non-intuitive might be happening.

So, to confirm: each heat map is a row/column of the spectrum for the line of pixels (the top heat map being a spectrum for a horizontal line of pixels, and the one on the right, for a vertical line of pixels) formed by the common edge between the heat-map and the image, when you place one face perpendicularly and edge-on on the other.

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As for the seismometer - what you describe sounds far too complex and energy-intensive for a small rover, possibly even potentially harmful to the rover, and I think the data would be far less able to resolve near-surface structures.

Harmful how? Reflected vibrations potentially leading to RUD? Or even S(low)UD? But the rover withstands launch! I wasn't considering anything more powerful/complex/power-hungry than a concrete vibrator anyway. There doesn't have to be a strong vibration coupling between instrument and rest of rover either. Consider a sensor head linked to rover only by power/data cables... transported from a stowage location on the rover to the surface by the arm...

As regards the relative merits of each technology - from a science perspective - browsing through this paper (which compared the two at a Controlled Archaeological test site) I think that acoustic interrogation would yield direct geomechanical information (as opposed to having to go from di-electric properties to mineral composition to geological conditions required for formation of such minerals), given that the velocity of propagation is dependent on the grain size, confining pressures, elasticity and grain sizes etc.

Plus, I know that the moon is essentially regarded as dead (in terms of geology) - but an acoustic sensor will be able to function in a passive mode too. Maybe monitor impacts, moonquakes (tidal stretching of the moon due to the ellipticity of its orbit around Earth being a periodic stressor perhaps) etc.

However, all that's hand waving. OTOH the paper does mention 1) detector size advantages for GPR 2) the relative ease of coupling EM waves to the soil3) and that the acoustic method was susceptible to confusion from multiple reflections (though I'm hard pressed to think about a natural lunar process that results in heterogenous polygons with faces at all sorts of angles to wave propagation)

Having said all that, there doesn't seem to be a large difference in resolution. 0.34m (GPR) vs 1m (SRI) -- for their chosen frequencies, and assorted conditions. 3x is atleast the same order of magnitude, and the SRI value can potentially be increased. I'm also inclined to think that the requirements on the processing electronics would be quite a bit more stringent for GPR, not least because it would require higher clock speeds.

I have used GPR on several occasions, and shallow seismic once, GPR it has several advantages over seismic that add up in this context.

1) It does not need good ground connection, GPR uses antennae on or just above the ground surface (as here). Seismic needs to have at least one geophone on the ground, and also a signal generator, such as a mechanical or muscle power hammer, or small explosive charge, making contact with the ground. Seismic is therefore much more mechanically complex and is a stop-start operation. GPR works on the move, the units I have used have either operated from a hand-towed cart (me being the donkey) or on a snake towed at 5 kph behind a two seater ATV. So all in all GPR is simpler to deploy and operate compared to seismic.

2) GPR is probably easier to miniaturise than seismic, a good thing for a rover of any size.

3) Under lunar conditions I would expect excellent penetration with GPR, probably better than a small seismic of comparable dimensions. If am reading the small diagram correctly they are seeing down to 100 m, which exceptional for such a small unit. GPR transmitters emit over narrow frequencies so can be tailored to specific depths you are interested in. I note that in the article it says two frequencies, which would be useful.

4) I have never heard of a seismic survey instrument being used for seismic monitoring. I don't know if this is even possible, seismic surveys and earthquakes generate signals in quite different frequencies.

I note that GRP was considered for the MERs at one stage. One GPR unit I have played with was built as a prototype for JPL, and very Heath Robinson it was too. But it was dropped because of two much electrical interference from other systems. ESA has a GPR on the ExoMars rover WISDOM).

Looking at the image there seems quite a bit to see. There is a shallow (down to ~30 m?) zone of strong, chaotic reflectors, probably the regolith. Below this is largely homogeneous unit to 80 m, and below that a slightly more heterogeneous unit, these may be stacked Mare basalt flows.

"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

While we wait again for more images and info from China of Change-3 lander and Yutu rover on Mare Imbrium I have been playing around with 3D Anaglyphs for Change3 lander and rover- not the best since original images not that great for 3D use. Maybe later images may be better for using ?

Panorama taken between Dec 17 - 18 by the lander (click to enlarge), seems like the news agency cropped image into multiple pieces without providing the panorama in its original quality, I tried to put them together. Source here.

I have been playing with some numbers concerning the "daytime" at the Chang-E 3 landing site. There is a parameter called the Sun's Selenographic Colongitude which can be found in many astronomical tables.

Thanks for that link to the lunar ephimerides. As an older paduan, I have much to learn.

No, each face of the cube is an image of the surface in that wavelength. Follow one pixel all the way down the stack and you get a spectrum for that pixel.(snip)

Not quite.Two opposing and parallel faces of the cubes are the image in the longest and shortest wavelengths. Each parallel plane in the cube is the same image in an adjacent color. As Phil stated, drilling through any pixel in a direction perpendicular to the monochromatic image does give the spectrum of that pixel. A plane in that direction is the collection of spectra for a full column or row of the image.

Some imaging spectrometers, like the LEISA detector on the Ralph instrument on New Horizons, produce a hyperspectral data "parallelepiped". The same principle applies to planes in the middle, with a full image at specific wavelengths, but at the ends the images are restricted to smaller and smaller frames. For LEISA these will be images of dark space, and will be truncated from the data set. I do not know which technique is employed by the imaging spectrometer on Chang-e, but it is probably the former.

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What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Couple more days then the Sun will disappear from Mare Imbrium leaving Change'3 and Yutu in dark again for many days.

So, we have gone a couple weeks and no "new" images or solid science data from Chinese Space Agency apart from a panorama built up from earlier images and a brief statement they deployed "arm" (At least I have not seen any on space forums or main news outlets).

Of course, they are under no obligation to release information but I think they are missing a PR opportunity here . And, if no further information forthcoming we might start to construe its failed ?

Perhaps what we can expect as the mission proceeds is a summary of events during each lunar day, at the end of the day. The most interesting thing to look forward to right now will be a new LRO image very soon, so we will know for sure where the rover is. Big move, all is well. Little move, not so good.